EP0066410A1

EP0066410A1 - Thread cutting device for sewing machine

Info

Publication number: EP0066410A1
Application number: EP82302537A
Authority: EP
Inventors: Kikuo Mori; Rokuro Yokota; Masashi Teramoto
Original assignee: Pegasus Sewing Machine Manufacturing Co Ltd
Current assignee: Pegasus Co Ltd
Priority date: 1981-06-02
Filing date: 1982-05-18
Publication date: 1982-12-08

Abstract

A thread cutting device for sewing machine having a thread catcher and a cutting blade. Linked with the operation to close sewing, a thread catcher operating device is connected with the driving shaft of looper, so that the thread catcher is moved forward by utilizing the driving shaft as a driving source until such time as is immediately before the looper reaches the most advanced position to stop. immediately before the looper stops its movement at the most advanced position, the connection between the operating device and the driving shaft is released, upon which the thread catcher is returned by the action of the spring, catches the needle thread and the looper thread, draws them to the position of the cutting blade and cuts them.

Description

The present invention relates to a thread cutting device for use in sewing machine. More particularly, it relates to a thread cutting device adapted for use in a double chain stitch sewing machine and a flat seam sewing machine wherein the thread catcher moves reciprocally between the needle plate and the looper to catch the needle thread and the looper thread stretched from the terminal seam to the looper, pull them to the position of the cutting blade, and cut them in cooperation with the cutting blade.

PRIOR ART:

_'The thread cutting devices of the abovementioned type are well known in the double chain stitch sewing machine. In such known thread cutting devices, usually there are combined a thread tension releasing device designed to release the action of the thread tension adjuster and a thread draw-off device for drawing out a moderate amount of thread from the spool before cutting the thread. Cutting of thread with such a device is conducted in such sequence that, after the stoppage of sewing, i.e., after the needle comes to the top dead center and the looper comes to the most advanced position and the seam forming mechanism stops its movement, the thread tension releasing device and the thread draw-off device are sequentially actuated, followed by the reciprocating motion of the thread catcher. Typical examples of such a type of thread cutting device are disclosed in U.S. Patent Nos. 3,489,115, 3,532,065, and 3,424,117.
In the sewing machines, especially in the industrial sewing machines, increment of speed in sewing operation is demanded, and it is desirable even on the above described known thread cutting devices to curtail the time of interval from the stoppage of sewing to the cutting of thread.
Also, in the known thread cutting device, there has hitherto been used solenoid and air cylinder as the driving source for thread tension releasing -device, thread draw-off device, and thread catcher operating device. In case of using the former solenoid, it is required to employ a solenoid having a large load capacity for actuating the thread catcher. On the other hand, when the latter air cylinder is used, complicated piping and compressors are required, so that the construction becomes complicated.
In the abovementioned known thread cutting devices, there is a tendency that when the thread catcher catches the needle thread and the looper thread and draws them to the position of the cutting blade, the thread catcher is apt to cause torsion by the tension of the both threads, especially of the needle thread. Therefore, when the thread catcher under the torsional deflected condition is engaged with the cutting blade, there is provided a gap between the thread catcher and the cutting blade to prevent normal practice of cutting of thread.
The above tendency has been more conspicuously seen with the coarser thread count and with the larger number of needle threads to be applied to the thread catcher as in the three-needle or four-needle sewing machine.
The above defects of thread cutting have hitherto been covered by employing a method of increasing the spring pressure of the clamp for holding the thread catcher with the cutting blade, or adjusting the torsion of the thread catcher for the cutting blade or adjusting their mounting so as to prevent a gap from being formed between the cutting blade and the thread catcher. However, in the case of the method of increasing the spring pressure of the former, even if the fabric is advanced with the start of sewing, the end of the looper thread is not easily drawn off from the clamp, with the result that the starting seam tended to shrink or the idle end of the looper thread might remain long at the starting end of sewing. Besides, friction at the time of operating the thread catcher held by the clamp became large, so that, in case of carrying out the return motion of the thread catcher by a spring, use of a strong spring was necessitated, with the consequential requirement of a large driving force for moving the thread catcher forward, and a large size for the driving device such as solenoid or air cylinder. In case of the.employment of the latter, its adjustment involves extreme trouble.

SUMMARY OF THE INVENTION

The present invention is to provide a thread cutting device for sewing machine comprising a thread catcher for catching thread, an operating device for causing reciprocating movement to said thread catcher between the needle plate and the looper, a cutting blade to cut the thread caught by the thread catcher in cooperation with the thread catcher, and a changeover device to cause the thread catcher operating device, which is normally standing still independent from the driving device for the sewing machine, to be subordinate to the driving device of the sewing machine. By means of the changeover device which is operated linked with the operation to close sewing, the thread catcher operating device is rendered to be subordinate to the driving device of the sewing machine so as to/operate the driving device of the sewing machine as the driving source. According to this device, in the course of the period in which, at the end of the sewing, the needle rises from the bottom dead center to the top dead center, the thread catcher is operated linked with said movement, and after arrival of the needle at the position near the top dead center, cutting of thread takes place.
Accordingly, an object of the present invention is to provide a thread cutting device which permits curtailing of the time until the thread cutting is made after the closing operation of sewing and thereby increasing the speed of sewing operation.
Another object of the present invention is to.utilize the driving device for the sewing machine as a driving source for the thread catcher operating device and to eliminate the need for any special device for reciprocating the thread catcher such as solenoid or air cylinder.
A further object of the present invention is to utilize the driving source for the sewing machine which is the driving source for the thread catcher operating device as a common driving source for the thread tension releasing device and the thread draw-off device to be combined with the thread cutting device and to actuate them prior to the cutting of thread.
A still further object of the present invention is to ensure cutting of thread even when the thread catcher is distorted by the tension of the thread applied to said catcher.
These objects can be attained by rotatably axially supporting the cutting blade, because it is possible thereby not to provide any gap to.the cutting portion between the thread catcher and the cutting blade, as the cutting blade rotates according to the torsion of the thread catcher that may be caused.
Other objects, features and advantages of the present invention will become apparent from the following description of embodiment taken in reference to the appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a pictorial view of a sewing machine including the thread cutting device according to the present invention;
Figs. 2 and 3 are perspective views of the thread cutting device according to the present invention, showing it to be in a non-cutting position and in an extended, position, respectively;
Fig. 4 is an elevational view of the thread catcher operating mechanism as shown in Figs. 2 and 3;
Fig. 5 is a partially cut top view of the thread catcher operating mechanism;
Figs. 6A, 6B, 6C and 6D are respectively the views to show the sequence of operation of the thread catcher at the time of cutting of thread;
Fig. 7 is a perspective view of the device in which the cutting blade is made movable to the cutting position;
Figs. 8, 9, and 10 are views to show the different disposition of the thread during the respective intervals of the cutting action on the device shown in Fig. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 1 shows a double chainstitch sewing machine designed to form double chainstitches by the cooperative actions of the needle 13 and the looper 14. On the standard 15 there are provided a tension releasing device comprising the known thread tension adjustor 16 and a sliding plate 17 and a thread draw-off device comprising the thread draw-off part 18.
The sliding plate 17 and the thread draw-off part 18 are connected in one body so as to move up and down by the rotation of the lever 19. The lever 19 is connected with the thread cutting device generally indicated in numeral 21 arranged in the bed 20 mediated by the link mechanism 22.
Accordingly, the sliding plate 17 and the thread draw-off part 18 are moved up linked with the operation of the thread cutting device, by which it invalidates the effect of the thread tension adjuster 16 to release thread tension, and on the other hand pulls up the thread by a certain length to effect thread drawing off from the spool (not shown).
The thread cutting device 21 is provided with a cutting blade 25 and a thread catcher 26, as shown in Figs. 2 and 3. The axle 30 is rotatably supported by the guide member 27 mounted to the machine frame (not shown), and stopped with the plate spring 31 by the screw 32 onto the block 28 of the axle 30. Axial shift of the axle 30 is regulated by the block 28 and the pin 29. The slide bar 33, along with the axle 30, is slidably supported to the guide member27, which is mounted to the slide bar 33 by the screw 34, to be moved. forward and backward under the condition pressed to the cutting blade 25 by means of the spring plate 31.
In cutting the thread, by the forward movement of the lever 38 which is pivotally supported to the machine frame at its middle portion and slidably fitted in the slot 36 formed at its end with a pin 37 fitted to the above slide bar 33, i.e., by the clockwise rotation of the lever 38 in Fig. 2, the thread catcher 26 is advanced (Fig. 3), and is retracted by the return movement of the lever 38, and on the way of its retraction, the thread catcher catches the needle thread and the looper thread, draws them to the cutting blade 25, and cut them in cooperation with the cutting blade.
The cutting blade and the thread catcher as described above are the same as those of the known devices, excepting that the cutting blade is rotatable. When the cutting blade is made rotatable, the cutting blade can rotate following after the torsion of the thread catcher, especially when torsion is formed by the tension of the needle thread at the time when the thread catcher catches the thread and pulls it, with the result that the blade edge is always kept in exact contact with the upper surface of the thread catcher without leaving any gap, so that the defective thread cutting attributed to the torsion of the thread catcher is evaded.
The thread cutting device further includes a mechanism for actuating the lever 38, on which description will be made hereunder.
On the brackets 42 fixed to the machine frame, there are mounted a guide shaft 43 and a movable shaft 44 in parallel, the guide shaft 43 being fixed to the bracket 42 and the movable shaft 44 in a slidable manner. To the movable shaft 44 are further fixed a block 46 connected with the aforedescribed link mechanism 22, a block 48 protrudingly provided on its lateral side with a pin 47, a guide block 49 with a fork being engaged with the guide shaft 43 for arresting rotation of the movable shaft, and a block 53 having at its top a pin 52 for engagement in a slot 51 formed at the other end of the lever 38. The movable shaft 44 is biased in the right direction in Figs. 2, 3, and 4 by a spring 55 fitted with the guide shaft 43 lying between the bracket 42 and the guide block 49,. and arrests the thread catcher 26 to its retracted position. The guide block 49 may act to arrest rotation of the movable shaft and also to adjust the strength of the spring 55 by adjusting its position of fitting to the movable shaft 44 to either right or left. If there is no need to adjust the spring force, there may be formed on the block 53 a fork riding on the guide shaft 43 so as to provide said block with the function of the guide block 49, i.e., the function to arrest rotation of the movable shaft.
A bell crank 58, having at its end a fork portion 57 for slidably fitted over the pin 47 of the block 48 is pivotally supported in rotatable and slidable manner on the shaft 59 protrudingly provided from the bracket 42, and provided with a fork end 60 at the boss portion and a roller 61 at the other end.
The bell crank 58 is shifted to the axial direction of the shaft 59 according to the rotation of the lever 63 which is slidably fitted in the fork end 60 of the boss portion to shift the roller 61 to the acting or non-acting position of the arm 66 fixed to the looper drive shaft 65 which causes reciprocating movement to the looper 14 in the direction to intersect at right angles to the direction of advance.
Now, the arm 66 is a position separated from the roller 61 when the looper 14 is retracted to the farthest, i.e., when the looper 14 is positioned at the right end on the face of Fig. 1 (ref. Fig. 4), so that the shifting of the shaft 59 of the bell crank 58 is not impeded, and the arm 66 is engaged with the roller 61 on the way of advance of the looper. Accordingly, the bell crank is rotated with the differentiated timing from the looper movement.
The above lever 63 fixed to the vertical shaft 68 which is pivotally supported on the bracket 42 (see also Figs. 4 and 5) causes the above bell crank 58 to be in contact in spring force.with the head portion 59a of the shaft 59 by means of the spring 69, thereby making the roller 61 positioned normally on the non-acting position of the arm 66.
In order to have the lever 63 rotate against the action of the spring 69 to shift the bell crank 58, a solenoid 71 is provided. It is so designed that, by the excitation of said solenoid, the plunger 73, engagable with the pin 72 which is protrudingly provided on the lever 63, is projected to push the pin 72.
As described above, the solenoid 71 pushes the bell crank 58 on its excitation and shifts the roller 61 to the acting position of the arm 66. The roller 61 requires to be held at the acting position of said arm against the action of the spring 69 during the time when the looper 14 advances nearly to the most advanced position, i.e., while the arm 66 rotates in clockwise direction..
To this end, it may be possible to keep,the excitation of solenoid 71 while the arm 66 rotates in the clockwise direction. Preferably, there is provided a restraining device comprising a latch lever 76 fitted to the upper end of the vertical shaft 68 and an engaging member 79 having nearly L shaped cross section which is pivotally supported by the shaft 77 fitted to the block (not shown) mounted onto the machine frame and normally having its one end 79a elastically in contact with the upper surface of the latch lever 76.
According to this restraining device, when the solenoid 71 is excited and the latch lever 76 is rotated with the lever 63, one end 79a of the above engaging member is disengaged from the upper surface of the latch lever to be lowered by the action of the spring 78 and is engaged with the lateral end face of the latch lever, by which movement of the latch lever 76 tending to return by the action of the spring 69 is arrested (Fig. 5).
In order to prevent the engaging member 79 from excessively rotating during its rotation by the action of the spring 78 to cause the end 79a of the engaging member disengaged from the lateral end surface of the latch lever and go excessively low, it is desirable to provide a stopper (not shown) to control rotation of the engaging member 79 to a certain limit.
An end 79a of the engaging member for inhibiting the return movement of the latch lever by engagement with the lateral surface of the latch lever is lifted up when the other side 79b of the engaging member is pushed by the foremost end 44a of the movable shaft 44 which moves in the axial direction by the rotation of the bell crank 58 caused by the arm 66 and is disengaged from the end face of the latch lever (Fig. 4). Immediately after the disengagement of an end of the engaging member from the lateral end face of the latch lever, the latch lever sets back the lower face of the engaging member by the action of spring 69. At the same time, the bell crank also moves in an axial direction and returns to its original position, and the roller 61 is put to its original position not to act the arm 66.
Then, the bell crank is rotated to return along with the return action of the movable shaft 44 under the action of the spring 55.
In the above described embodiment, the thread catcher is designed to be operated by the looper drive shaft. However, it may be operated from other moving part of the sewing machine such as a feed shaft which causes to move the feed dog back and forth.
The sewing machine furnished with this device is incorporated with a driving motor equipped with a needle positioner of the known type. When an operating means such as for example a treadle is operated, the solenoid 71 is excited and the needle 13 is lifted from the bottom dead center to reach the top dead center, and the looper 14 is advanced to reach the most advanced position, after which the movement is stopped.

OPERATION OF THE MECHANISM

When, in order to stop the sewing machine, an operating means such as a foot pedal is operated, the solenoid 71 is excited, and its plunger 73 pushes the pin 72 to rotate the lever 63, by which it moves the bell crank 58 in an axial direction to move the roller 61 to the acting position of the arm 66. At this time, a side 79a of the engaging member 79 is disengaged from the upper surface of the rotating latch lever 76 to rest on the lateral side surface thereof to keep the roller 61 remaining on the above acting position. Then, simultaneously with the rise of the needle from the lower dead center, the looper drive shaft 65 is rotated, by which the looper 14 starts.to advance from the rightmost position of Fig. 6A and the arm 66 rotates, and in the course of its rotation it is engaged with the roller 61 to rotate the bell crank 58 and causes a forward movement to the movable shaft 44.
The forward movement of the movable shaft causes a rotary movement to the lever 19 via the link mechanism 22, by which the slidable plate 17 and the thread draw-off part 18 rise to effect release of thread tension and drawing off of thread from the spool as aforementioned. Simultaneously with this, the lever 38 is rotated to slide the slide bar 33, and causes the thread catcher 26 to advance from the condition of Fig. 6A in a manner to follow after the looper 14 (Fig. 6B). When the looper 14 advances to reach its most advanced position, the thread catcher also completes its advance (Fig. 6C).
When the thread catcher is about to terminate its advance, the foremost end 44a of the movable shaft pushes the other end part 79b of the engaging member, raises its one end 79a to disengage from the latch lever 76, and releases the restraint of said lever. By this, the lever 76 returns by the action of the spring 69, upon which the bell crank 58 is moved back in an axial direction, the roller 61 is returned to the non-acting position of the arm 66, and the engaged condition with the arm 66 is released.
In consequence of the above, the movable shaft 44 is moved back by the action of the spring 55 while causing the bell crank 58 to rotate. On one hand, this causes the lever 19 to rotate via the link mechanism 22, thereby causing the slidable plate 17 and the thread draw-off part 18 to descend to effectuate the action of the thread tension device 16 and loosen the needle thread and the looper thread, and on the other hand it causes to rotate the lever 38 to retract the thread catcher 26. The thread catcher 26 catches during its retreating movement the needle threads N₁, N₂and the looper thread No which are extended from the looper 14 to the terminal end of sewing, draws them to the position of the cutting blade 25, and cuts them in cooperation with the cutting blade (Fig. 6D). Thereafter, the thread catcher is returned to its original position.
Figs. 7 to 10 show a device in which the cutting blade is advanced to the cutting position and thread cutting is conducted at a position near the seam forming zone. To the guide member 101 a shaft 102 is supported in a slidable and rotatable manner, and a slide bar 103 is fitted in a manner to be slidably operated by the lever 105 as in the case of the afore-described slide bar 33. To the block 107 for fixing the cutting blade 106 of the shaft 102, a pin 109 which is to be slidably inserted in the pin hole of the fixing member 108 is protrudingly provided, and on the pin 109 a spring 110 is fitted. By these engagements, the block 107 is biased in a manner to be in contact with the engaging in a manner mounted to the slide bar 103 together with the thread catcher 112. Accordingly, at the time with the thread of the slide bar 103, the cutting blade of the advance of body with the thread catcher 112. At advances in one retreat of the slide bar 103, it recedes with of the thread catcher, pressed by the engaging piece 113 wich is in contact with the block 107. In order to stop the cutting blade 106 which advances with the thread catcher at a certain position, the shaft 102 is protrudingly provided with a stopper pin 115 which is engaged with the guide member 101.
According to this device, because the thread cutting is made at the position near the seam forming zone, the length of the idle end of the thread extended from the terminal seam end can be shortened. However, the cut thread, especially the looper thread, should be kept in a held state during the required time for the subsequent start of sewing, otherwise, the cut thread is apt to slip out from the looper under the action of the looper thread cam take-up. In order to dissolve this problem, there is provided a clamp which is in elastic contact with the cutting blade or the thread catcher, so as to clamp the cut thread end in cooperation with the cutting blade or the thread catcher. When the spring pressure of the clamp is weak, the looper thread may have a risk of slipping out from the looper. Reversely, if the spring pressure is too strong, even if the fabric is advanced along with the start of sewing, the looper thread end is not easily released from the clamp, so that troubles are apt to occur such that the starting seam may shrink or the idle end of the looper thread remains long at the starting end of sewing. It is extremely troublesome and difficult to adjust the spring pressure of the clamp in order to prevent such inconvenience. Thus, it is desired to dissolve a risk for the looper thread to slip out from the looper and to free the cut end of the looper thread without being clamped.
In order to practise as above, the thread draw-off part 120 having a thread eyelet 118 for leading the looper thread No between the looper thread cam take-up 117 and the looper 14, is formed on the engaging piece 113. And, into a looper thread stopper 121 is inserted the looper thread, which is pulled by the thread draw-off parts 120 which advances in one body with the thread catcher on the forward movement of the thread catcher at the time of the thread cutting. The looper thread stopper 121 is to hold the looper thread until the next first seam is formed after the thread cutting.
The looper thread stopper 121 comprises a nearly laid U shaped fitting 124 which is mounted at the lower lateral end portion to the looper thread cam take-up 117 by means of-the screw 123 and a wire spring 126 which extends diagonally upward from one end part mounted to the screw 123, with its other side bent from the middle part, being elastically set in contact with the upper side of the fitting 124 and its foremost end projected from the slit 125 of the fitting 124. During the normal sewing operation, the looper thread stopper is disposed at the offset side of the looper thread path between the looper thread cam take-up and the thread guide 128 so as not to be engaged with the looper thread.
At the time of cutting the thread, by the forward movement of the lever 105 at the outset, the cutting blade 106 and the thread catcher 112 advance in one body in a manner to follow after the looper 14, and the thread draw-off part 120 also starts to pull the looper thread N₀ positioned between the looper thread cam take-up 117 and the thread guide 128 in the direction of advance of the thread catcher (Fig. 8). After the stoppage of the advance of the cutting blade 106 by the engagement of the stopper pin 115 with the guide member 101, only the thread catcher 112 further advances, and the looper thread pulled by the thread draw-off part is inserted between the wire spring 126 and the upper side of the fitting 124 of the looper thread stopper 121 (Fig. 9). The thread catcher, after having reached the most advanced position, retreats on the return movement of the lever 105, and on the way of its retreat catches the needle threads N,, N₂ and the looper thread No which are extended from the looper 14 to the terminal seam, pulls them to the cutting blade 106 positioned at the cutting position, and cuts them. The cut needle threads _N1, _N2 and the looper thread No are immediately released without being held, and thereafter the catcher and the cutting blade return to the original positions (Fig. 10). Due to the retreat of the thread draw-off part during this time, the looper thread which had been pulled is loosened, and the looper thread inserted between the upper side part of the fitting and the wire spring is held in the inserted position. Such holding of looper thread is maintained until the next sewing operation is started and the first seam is formed. Therefore, the looper thread cam take-up 117 just draws out the looper thread from the spool while absorbing the loosening of the looper thread on the spool side from the looper thread stopper 121 in the initial seam forming period, and it does not reel in the looper thread on the looper side of the looper thread stopper.
Accordingly, as described above, even if the cut looper thread end is freed, the looper thread does not slip out from the looper. When the first seam is formed, the thread end comes to be caught by the said seam, and, during the next seam forming period, as the looper threads are simultaneously pulled under tension on both sides of the looper thread stopper by the actions of the looper and the looper thread cam take-up, the looper threads slip out from the looper thread stopper.
Thereafter, until the subsequent cutting of the thread, the looper thread is not held.
Although certain preferred embodiments have been shown and described in detail, it should be understood that many changes and modifications may be made therein without departing from the scope of the appended claims.

Claims

1. A thread cutting device for sewing machines comprising a cutting blade and a thread catcher designned to catch the needle thread and the looper thread streatched from the looper to the terminal seam end by reciprocating between the needle plate and looper, draw them to the position of the cutting blade and cut them in cooperation with the cutting blade, characterized by comprising an operating device for reciprocation of thread catcher which includes the first bias means for biasing the thread catcher in a direction of return, and a changeover device which is so designed as to connect the operating device with driving means for the sewing machine during the period immediately before stoppage of the needle in the course of its rising from the bottom dead center to the top dead center and to release the connection between the cooperating device and the driving means immediately before stoppage of the needle at the top dead center, said thread catcher moving forward resisting the action of said first bias means by utilizing the driving means as a driving source by the connection of the operating device with the driving means and moving back by said bias means after rellease of the connection of the operating device to the driving device.

2. The thread cutting device according to Claim 1, wherein the operating device includes the means supported to the fixed shaft in rotatable and axially movable manner; the second bias means which normally bias said means to the non-operating position, said means being caused to shift to the operating position or to the non-operating position of the driving means by the movement in the axial direction of the fixed shaft; and the transmission means for transmitting to the thread catcher the movement of said means rotated by said driving means after shifting to the operating position of driving means; and the changeover device includes a changeover means which is operated in linkage with stoppage of the sewing machine operation and shifts said means to the operating position against the action of the above second bias means.

3. The thread cutting device according to Claim 2, wherein the changeover device includes a restraining means which retains the means moved to the operating position to its position until immediately before stoppage of the driving means.

4. The thread cutting device according to Claim 3, wherein the restraining means includes a latch lever which is subordinate to said means and changes its position in linkage with the movement of said means and an engaging member which is to be engaged with the latch lever at the time of the removal of said means to the operating position to arrest its return movement, and to release its engagement with the latch lever immediately before termination of rotation of said means on stoppage of the driving means.

5. The thread cutting device according to Claim 4, wherein the latch lever is connected in one body with the lever for moving said means in an axial direction, and the transmission means includes a releasing member for releasing the engagement of the engaging member with the latch lever.

6. The thread cutting device according to Claim 2, wherein the changeover means is a solenoid.

7. The thread cutting device according to Claim 2, wherein the lever for operating the thread tension releasing device and the thread drawing off device is connected to the transmission means by means of the link mechanism.

8. The thread cutting device according to Claim 1, wherein the looper thread stopper is provided in a'position not engaging with the looper thread alongside the looper thread course between the looper thread cam take-up and the looper, and the thread catcher is provided with the thread drawing means so as to form one body, so that the thread drawing means which reciprocates with the thread catcher draws the looper thread between the looper thread cam take-up and the looper to engage it with said looper thread stopper, and the looper thread caught is held by said looper thread stopper until the first seam in the subsequent stitching is formed.

9. The thread cutting device according to Claim 8, wherein the looper thread stopper comprises a nearly laid U shaped fitting with one end on the lower side fixed and a spring which is bent in an obtuse angle from the middle part with one end fixed and with the other side elastically set in contact with the upper side part of said fitting.

10. The thread cutting device according to Claim 8, wherein the cutting blade is movable to the cutting position near the seam forming zone.

ll. The thread cutting device according to Claim 1, wherein the cutting blade is supported in rotatable manner according to the torsion of the thread catcher.